Cleaning the Greenhouses
21st Oct 1999
The trouble at this time of year is that so many things need to be done at the same time, particularly constructing new things as well as completing the clear-out that's vital to prevent pest and diseases from taking a hold. The tomatoes have now all been removed and the stalks will be used as green material in my leek bed, coupled with seaweed from the nearby Menai Straits.
The main job now is to remove everything from both greenhouses and give them a real clean out as I shall soon be requiring them for leek bulbil propagation and, before we know it, onion sowing time will be upon us. The leeks and exhibition onions for Chelsea Show are really growing well; they were started off towards the end of July and are now in 4 pots at the University greenhouses at Bangor. However don"t be tempted to sow your leek and onions early as you will only have major problems later on; I shall cover these at a later date.
This year the tomatoes grew in the new wooden box that I constructed on the greenhouse concrete floor and, until botrytis started playing havoc with the crop, they were really looking well. Frank Mercer, from the Wirral, is a very experienced grower who has always grown good specimens, is rarely bothered with this disease and offers the following tip. According to Frank, the reason we have problems is that we try to grow too many plants in a given space with the consequence that the foliage touches and rubs against each other, spreading the disease about. In his greenhouse border Frank will only plant one row on either side, not two, and he will leave sufficient room between each plant so that when fully grown the foliage is barely touching each other. This is advice worth listening to; why plant twenty four good quality plants that succumb to the disease leaving you scraping the barrel for one decent dish. Would it not be better to plant a dozen healthy plants in the above manner so that you can easily look after them, they'll be healthier and every truss will offer you clean tomatoes that you can use in many shows.
The compost that was inside the box will now be removed and incorporated into the trenches for leeks and onions and the whole timber work and the concrete floor area will be washed clean. The next step is the annual ritual of checking up on the wiring just in case something has gone wrong over the growing season. In my case I don"t envisage too many problems as the whole wiring system was renewed over 2 years ago when one of my greenhouses collapsed after a tree fell on top of it.
The next stage is to thoroughly wash down all the glass,the glazing bars in between the panes of glass and the whole floor area using a strong dilution of Armillatox. One word of warning; when you do this, always isolate your power supply as water and electricity certainly don't mix. After the power has been isolated, cover over all the switches with an absorbent cloth such as an old towel and then cover that with a polythene bag. It may appear trivial but you certainly don't want to take any risks with electricity.
It's very important for me to make sure at this time that my thermostats are all working properly and I have three to check out. The first is obviously the one on my Parwin fan heater, a relatively new model that has the thermostat on the end of an extended lead rather than as part of the heater itself. This means that your thermostat can be positioned at bench level or root level where the temperature needs to be controlled positively. Switch the heater on and set the thermostat at 50°F; with your maximum/minimum thermometer positioned just above the plants, you can then check the temperature at which the heater is switching off as well as the temperature at which it cuts in again.
The next one to check is the rod thermostat in the propagating bench to make sure that it's working and not over heating. This can also be checked over a period of a few days by inserting a soil thermometer into the sand surrounding the heating cables. Finally I have a fan that's positioned just above the plants at one end of the bench with the purpose of moving the air around. A second fan is positioned at the far end which switches on at the same time to remove any excess heat from the greenhouse. These work by means of a reverse thermostat which operates differently to the others as it switches on when the temperature is rising whilst the heating thermostats switch on when the temperature is dropping.
If you intend to grow vegetables to the highest standards for exhibition, you will need to consider some form of electrical set up like mine. Please do consult first with a qualified electrical engineer who will guide you through the do's and don'ts of heating and ventilating a greenhouse.
A handy guide for the novice grower who wants to start off with heating a greenhouse is the Greenhouse Expert by D G Hessayon. This is one in a series of the 'Expert Books' a highly acclaimed series that should be available from most good garden centres.